A transfer case is a part of a drive system for four wheel drive and all-wheel drive vehicles. The transfer case houses drive components that connect to the primary drive mechanism of the vehicle and transfers operative power to the front drive axle via a drive shaft associated with the drive components within the transfer case. Operative power is generally transferred from the primary drive mechanism to the drive components within the transfer case using a set of gears or a chain drive mechanism.
On some vehicles, including particularly commercial trucks and tractors, a power takeoff mechanism (PTO) is provided to transfer engine power to another piece of equipment or an accessory device carried by the vehicle. Typically, the power takeoff mechanism transfers engine power from the transmission to a secondary implement or accessory device by a power takeoff shaft. The power takeoff mechanism is operable independently of the transfer of engine power through the transfer case. Typically, manual drive transmissions have provisions for connecting the power takeoff mechanism lower on the transmission, in which case the power takeoff shaft is more easily able to pass below the transfer case to deliver engine power to the remote secondary or accessory device. Customarily, automatic transmissions provide operative connection of the power takeoff mechanism to the side of the transmission. As a result, power takeoff shafts are usually provided with universal joints to enable the power takeoff shaft to circumvent the transfer case to deliver operative power to the secondary implement or accessory device located behind the transfer case, as is depicted in FIG. 2 in broken lines.
The routing of the power takeoff shaft below the transfer case creates clearance problems, as the power takeoff mechanism often become the lowest part of the drive mechanism. Furthermore, maintaining acceptable driveline angles within the universal joints can be problematic, as designing a power takeoff mechanism that will maximize ground clearance while minimizing the number of universal joints and the driveline angles required of the universal joints can prove to be difficult.
It would be desirable to provide a drive mechanism for a four wheel drive vehicle utilizing a transfer case that would allow for providing a power takeoff mechanism that would maximize ground clearance while minimizing problems with universal joints in the power takeoff shaft.